1. Field of the Invention
The present invention relates to an organic EL display panel and a method for manufacturing an organic EL display panel. In particular, the present invention relates to an organic EL display panel and a method for manufacturing an organic EL display panel in which a crosstalk can be prevented while a driving voltage is decreased and a luminescent efficiency is improved by forming a luminescent medium layer which has a plurality of layers, only within pixels.
2. Description of the Related Art
An organic EL element emits light by applying electrical current to a luminescent layer. The luminescent layer which is made of an organic luminescence material is formed between two electrodes facing each other.
In order to manufacture a reliable element efficiently, the thickness of a luminescent layer is important. When a luminescent layer is used for a color display, patterning with a high definition is necessary.
As an organic luminous material which forms a luminescent layer, a low-molecular material and a high-molecular material can be used. In general, a thin film of a low-molecular material is formed by a vacuum evaporation method or the like, and in this case, patterning is performed by using a mask which has a fine pattern. However, there was a problem that the larger a substrate became, the more difficult it becomes to obtain patterning accuracy. Moreover, throughput is poor since a film formation is carried out in a vacuum condition.
Then, recently, a method for forming a thin film by a wet coating method with a coating liquid which is made by dissolving a high-molecular material in a solvent has been practiced. A layer composition in which a hole transport layer and a luminescent layer are stacked from an anode side, i.e. a composition of two layers is usual, when a luminescent medium layer which includes a luminescent layer is formed by a wet coating method using a coating liquid of a high-molecular material. At this time, in order to provide a color panel, it is necessary to form different colors of a luminescent layer separately, using an organic luminescent ink which is made by dissolving or stably dispersing an organic luminous material having respective colors of red (R), green (G) and blue (B) in a solvent.
However, in either case that an organic luminous material of a low-molecular material or a high-molecular material is used, separated applications of materials other than a luminous material are not generally performed. Therefore, as FIG. 5 shows, a solid film as a common layer for all colors is sufficient and high definition patterning is not necessary. A film of polymer formed by a wet coating method, a film of a low-molecular organic material formed by a vacuum evaporation method and a film of an inorganic material formed by a vacuum evaporation method, sputtering, CVD (CHEMICAL VAPOR DEPOSITION) or other film formation methods can be used as a layer other than a luminescent layer. At this time, when a film of an inorganic material which has a high electrical conductivity is formed in order to decrease a driving voltage, an electrical current leaks into an adjacent pixel and a film of an inorganic material which essentially does not emit light between pixels. Therefore, there was a problem of a crosstalk in which a space between pixels and an adjacent pixel emitted light.
To solve this problem, a crosstalk can be prevented by controlling an electrical current leak by using a material which has a low electrical conductivity. However, there still remained a problem that an electrical power became large by increasing a driving voltage or by a decrease in luminescent efficiency caused by a decrease of an inlet flow of a hole from an anode. Although film resistance can be controlled by making the thickness of an inorganic material thin, it becomes easier for the EL to short out by making the thickness of an inorganic material thin. Therefore, there was a problem that the yield rate of production decreases.
According to Patent Document 1 a technique is disclosed in which a film quality is changed for controlling an electrical current leak by processing a film formed on a confining wall with UV. However, there was a problem that the above technique was mainly effective for a hole transport layer made of an organic material and processing was complicated.
As shown in FIG. 7, the hitherto known organic EL display panel has, for example, a hole transport layer made of an inorganic material and a counter electrode formed on an anode. In the above, when a film of a hole transport layer made of a hole transport material of an inorganic material is formed on a display area, a pattern formation of a film is performed by a vacuum evaporation method, sputtering or CVD. However, when a solid film of a hole transport layer made of an inorganic material which has a high electrical conductivity is formed in order to decrease a driving voltage, an electrical current leaks into an adjacent pixel and a film of a hole transport layer made of an inorganic material which essentially does not emit light between pixels. Therefore, there was a problem of a crosstalk in which a space between pixels and an adjacent pixel emitted light.
The present invention relates to an organic EL display panel which has a plurality of luminescent medium layers including a luminescent layer and a method for manufacturing an organic EL display panel. In particular, the present invention relates to an organic EL display panel and a method for manufacturing an organic EL display panel in which a crosstalk can be prevented while a driving voltage of an element is decreased and a luminescent efficiency is improved.    Patent Document 1: JP-A-2004-158436